Altitude and rate of change measuring device and control for aircraft



July 20, w48- G. A. PHILBRICK ET AL 2,445,335

ALTITUDE AND RATE 0F CHANGE MEASURING DEVICE AND CONTROL FOR AIRCRAFT Filed May 3, 1941 4 Sheets-Sheet 1 muy 2o, 194s.

G. A. PHlLBRlcK ET AL 2,445,335 ALTITUDE AND RATE OF CHANGE MEASURING DEVICE AND CONTROL FOR AIRCRAFT Filed May 3, 1941 4 Sheets-Sheet 2 f ATTORNEYS July 20, 1948. G. A. PHILBRICK ET Al. 2,445,335

ALTITUDE AND RATE OF CHANGE MEASURING DEVICE AND CONTROL FOR AIRCRAFT Filed May 3, 1941 4 Sheets-Sheet I5 INVENTORS QeOrgeAPhilbricc BYJlan/a/zeron JUly 20, 1948 G. A. PHlLBRlcK ET AL 2,445,335

ALTTUDE AND RATE OF CHANGE MEASURING DEVICE AND CONTROL FOR AIRCRAFT Filed May 3, 1941 4 Sheets-Sheet 4 Patented July 20, 194g NITED STATES ALTITUDE AND RATE OF CHANGE MEASURING DEVICE AND CONTRGL FOR AIRCRAFT of Massachusetts Application May 3, 1941, Serial No. 391,678

15 Claims. l

The present invention relates to altitude measurement and rate of climb measurement and more particularly to improved method and apparatus for making such measurements and for utilizing such measurements for controlling aircraft, and other media.

The conventional altitude meter and rate of climb meter utilizing the change of atmospheric pressure with change of altitude to determine altitude or rate of climb have inherent inaccuracies, and one of the objects of the present invention is to provide an improved method and apparatus for obtaining substantially instantaneous altitude and rate of climb measurements in whichinaccuracies formerly accepted as inevitable are eliminated. Other objects will be in part obvious and in part pointed out hereinafter.

In the drawings,

Figure 1 diagrammatically represents a conventional rate of climb meter;

Figure 2 diagrammatically represents a rate of climb instrument embodying the present invention;

Figure 3 diagrammatically represents a rate of climb indicator and an altitude indicating instrument embodying the present invention; and

Figures 4 and 5 diagrammatically represent a control system embodying the invention.

A brief review of the operation of, and of the inherent inaccuracies in, the present conventional rate of climb indicator will aid in an understanding of the advance made by the present invention.

Referring to Figure 1, the conventional rate of climb meter is diagrammatically shown, without, however, the usual means for compensating for temperature and altitude errors. Such a meter utilizes the change in atmospheric pressure that takes place as an aircraft changes its altitude. A pneumatic capacitance or chamber l is connected with the atmospheric or barometric pressure through a restriction or pneumatic resisltance R so that the pressure in the chamber may equalize with the atmospheric pressure when the latter is` not changing. But when the atmospheric pressure is changing, the restriction causes the pressure in the chamber to lag behind the changing atmospheric pressure so that a pressure difference exists between that in the chamber and that of the atmosphere at least so long as the latter is changing. This pressure difterence is taken as an indication of the rate oi atmospheric pressure change and therefore as the rate of 'climb or descent.

`lz'teferring inmore detail to the drawing of Figure l, the pneumatic capacity chamber is connected through a restriction R and a tube 2 to the atmospheric pressure. The tube 2 terminates in a static pressure head 3 and extends to a suitable place on the aircraft where an accurate barometric pressure exists. Supported in the chamber l on a bracket li is a spring-loaded bellows 5 having a free or movable end 6, i. e. the free end of the bellows 5 in moving away from the xed end moves against a spring restricting action. The bellows is directly connected through the tube 2-to the atmosphere without any deliberately inserted resistance. The bellows, therefore, is exposed on one side to the atmospheric pressure P1 and on the other to the chamber pressure Pz, and expands and contracts in proportion to. the pressure difference (P1-Pz). rThe bellows 5 is provided with a suitable spring characteristic selected in accordance with the range of movement desired for the corresponding expected range of pressure difference (P1-Pz).

The chamber l is, of course, pneumatically tight except for its connection to the atmosphere through the resistance R. The free end 6 of the bellows 5 operates a suitable index pointer 1 which cooperates with a scale 8 visible through a window 9 to indicate the degree of expansion or contraction of the bellows 5 and so the rate of climb or descent.

An inherent inaccuracy of this instrument is that it actually measures the rate of change of the pressure P2 in the chamber l instead of measuring the rate of change of the pressure P1. Further, the pressure Pz lags behind the pressure P1 when the latter has a rate of change. Thus this instrument has an inherent lag which renders it inaccurate. In other words, it takes time for an accurately indicative pressure difference (P1-P2) to be established between the changing chamber pressure P2 and the changing atmospheric pressure P1. Thus, assuming that P1 is suddenly given a constant rate of change, time is required for the pressure P2 to acquire the same rate of change and for the pressure difference (P1-P27) to become constant, and since itis (P1-P2) that is used to indicate the rate of change oi P1, time is required to elapse before the instrument will indicate the rate of change of P1.

The larger the volume of the chamber l or the greater the resistance R., the greater is this lag. But if the volume is reduced or the restriction is reduced, `then the pressure diierence applied to the bellows 5 for a given rate of change of pressure P1 is reduced, and the large multiplication of motion then necessary to obtain a readable indication of the pressure difference introduces other inaccuracies.

In the present invention this inherent inaccuracy is substantially minimized by utilizing an auxiliary source of power to maintain a condition, such as pressure, equal to or in fixed linear relationship with the atmospheric pressure. Then the rate of change of the auxiliary condition due to rate of change of altitude is obtained by eiectively measuring the potential or the ow required to maintain the predetermined relationship between said condition and the changing atmospheric pressure. With this method.` oi measurement there is no undesirable inherent lag and the rate of change of the atmospheric pressure and so the rate of climb or descent is substantially instantaneously measured.

Referring to Figure 2, in which one illustrative apparatus for carrying out the method o-fthe invention is diagrammatically disclosed, mechanism is provided for maintaining a pneumatic pressure P3 in a chamber IIJ in a predetermined relationship to the atmospheric pressure Pr. In the present embodiment therelationship is a linear relationship which is a constantpressure diiference. This mechanism includes a suitn able source of auxiliary supply pressure (in the present embodiment a suction pressure Ps) connected through lines II and I2 to the interior of the chamber Il) so that a constant relationship, suchias a pressure diierence (P1-Pa) may be maintained between the pressure P3 in the chamber I and the atmospheric pressure P1. The suction pressure Ps may be obtained conveniently in aircraft from a Venturi tube in the external air stream. Suction pressures obtained in this manner may be of the order of` five inches of mercury or more below the prevailing barometric or atmospheric pressure P1.

For mechanical simplicity it is assumed in the present embodiment. that the atmospheric, pressure P1 surrounds the apparatus. In practice this could be obtainedby covering those parts susceptible to the surrounding pressure and conducting vthe pressure P1A to. the cover as in Figure 1.

The pressure P3 is varied to maintain the pressure difference (Pr-P3) constant by providing a restriction I8 in the suction line II, and then varying the pressure in the line |12v leading to the chamberV IIJ in accordance with the difference in pressure between the atmospheric pressure P1 and the chamber pressure P3. This is accomplished by providing a connection from line I2 to atmespherethrough line I3 and a stationary nozzle or relief port I4 supported onA a bracket I5 carried .by the chamber I0. Cooperating with the nozzle I4 is a bail'ie I6 carried by the-free end of a detecting bellows I1 suitably supported by thechamber It] and opening into it. Thus the bellows I-'l responds on the outside to the atmospheric pressure P1 and on the inside to the pressure P3, and so is made to respond to the prsure difference (Pr-P3). By providing the restriction I8 in line II ahead of the nozzle I4, the pressure in the line I2 may be varied over wider limits and the nozzle may be made smaller and the baffle more sensitive. Such a nozzle and baffle construction is so sensitive in its operation that minimum pressure is obtained in line I2 when the baiiie touches the nozzle and-maximum pressure isl obtained in line I2 when the baille is moved only one-thousandth of an inch from the` nozzle.

Withthis constructionthe bellows I1 expands and` contracts to cover and uncover the nozzle I4 4 to control the pressure in the line I3 and in the chamber IIJ so that the baille I6 is always in juxtaposition to the nozzle I4, i. e., is always maintained within a thousandth of an inch proximity to the nozzle. The operation may be outlined as follows: If P1 increases or starts to increase and the pressure difference (P1-P3) consequently increases or starts to increase, the pressure on the bellows Il increases, causing it to contract to uncover the nozzle I4, and the pressure in the lines i3 and I2 starts increasing with the result that the pressure P3 in the chamber I0 and in the bellows I1 increases to reduce the pressure difference and move the baille I6 back to juxtaposition -to thel nozzle. In this manner the pressure P3 is caused to increase in exact proportion to the increase in pressure P1. Likewise, if P1 starts to reduce, as when an aircraft starts ascending, bellows Il expands due to the reduction in the pressure difference (P1-Pa). The baille, therefore, moves closer to cover the nozzle causing the pressure in lines I3 and I2, and in the chamber IU, to start reducing so that Pa is caused to reduce at the same rate that P1 is reducing. This action is so rapid that an essentially constant pressure difference (P1-P3) is maintained, the deviation from the constant being acted upon while it exists as a rate rather than a measurable quantity.

The iixed relationship that is thus maintained at all times between the pressure P1 andthe.

pressure P3 may be determined by selection ofthe spring characteristics of the detecting vbellows I1. Thus if the bellows has zero spring characteristic the pressure difference maintainedzwouldbe zero. bellows with a relatively stili spring characteristic is used so that the pressure difference has a positive finite value. The position of the nozzle I 4 with respect to the baille I6 may be varied by` adjusting the nozzle toward or away from the baille and in this way the pressure diiierence (P1-P3) may be adjusted to be half of the maximum suction pressure, or any other fraction of it desired.v If the instrument is adjusted so that the pressure difference is half way between the maximum and minimum suction pressures then the instrument has the same potential to give the pressure P3 a rate of increase as it has to give the pressure Pa a rate of decrease.

The potential or the flow of air to and from. the chamber Ill necessary to maintain the pressure P3 in linear relationship with the atmospheric pressure P1 is measured by providing a measuring restriction I9 in the line I2. The restriction I9 is of such a size that with the availabley change of pressure in P4 .the pressure P3 is. caused. to follow the largest rate of change likely to beend countered in atmospheric pressure P1, whereby the pressure diierence (P1-P3) is maintainedV flow into or out of the chamber I 0 is proportional.

to. this pressure diierence. This pressure difference is measured by an indicating. spring-loaded bellows 20 connected to line I2 .so thatthe pres'-V sure P4 in the bellows 20 is the same as that existing in the lines I2 and I3. The bellowsA 20 isv made responsive to the pressure P3 and sa to (P4-P3): by mounting the bellows in the chamber I0.

Since the indicating bellows 2li indicates the rate of flow into or out of the chamber I0; and

In the present embodiment, however,` aV

since the rate at which the pressure P3 in the chamber I changes is proportional tothe rate of ow into or out of it, the indicating bellows 20 indicates the rate at which P3 changes. Since, as above described, Pa is maintained in a xed -linear relationship with the atmospheric pressure P1, the indicating bellows 2|) therefore indicates the rate at which the atmospheric pressure P1 changes.

The condition of the indicating bellows 20 is indicated by a pointer 2| supported inside the casing on a support 22 and cooperating with an index 23.` A link 24 connects the free end of the indicating bellows 2u and the pointer 2|. The portion of the chamber I0 in front of the pointer 2| is made transparent so that the pointer may be viewed. Whereas in Figure 2 the bellows 2|) is made to respond to the pressure dierence (P4-Pa), it might also be made to respond to outside of bellows 20 to the atmosphere and this pressure diierence might be calibrated to indicate rate of climb.

Referring to Figure 3, another embodiment of the invention is shown in which several features are included which improve and extend the operation over that obtained under some conditions by the apparatus shown in Figure 2. Thus, for example, in most practical forms of such an apparatus as shown in Figure 2 a proportioning effect is introduced by the operation of the baffle and nozzle, which proportioning effect may cause a variation in the relationship maintained between the pressure Pa and the atmospheric pressure P1 for diierent values of the atmospheric pressure, and for diierent values of the suction pressure Ps. This is overcome in the embodiment of Figure 3 by a relay system. The relay system also permits the baffle operating bellows to be made sti* so that errors due to the effects of gravity andlnertia are eliminated. Also, sudden variations in the suction pressure PS, which under practical operating conditions are almost inevitable, are eliminated by providing a pressure regulator in the suction line. The relay system also reduces the effect that sudden change of suction pressure would otherwise have on the measurement. In Figure 3, provision is made for obtaining the true barometric or atmospheric pressure instead of making the detecting bellows responsive as in Figure 2 to the cockpit pressure which frequently diners from the atmospheric pressure. And, since the tubing for conveying such a static pressure to the instrument introduces a lag between the true barometric pressure and the barometric pressure as received at the instrument, means are provided for compensating for this lag and for removing its effects.

Referring to Figure 3, the suction pressure Ps, instead of being connected directly to the restriction IB and nozzle I4, is connected through a spring-loaded bellows 25 and a port 26 located within the bellows. The connecting tube ||a connects the bellows 25 with the restriction I8 and the nozzle I4. The bellows 25 is exposed to approximately barometric pressure on the outside so that it responds to the diierence between the approximately barometric ambient pressure Pia and the suction pressure Ps1 within the bel-lows. It is provided with a spring characteristic such as to close oi the port 26 when the pressure difference goes below a predetermined value (Pia-Ps1) and to expand to open the port 26 when the pressure dierence rises above the value (Pia-Ps1). Thus a substantially constant relative suction pressure is maintained in the line Ila.

Instead of using nozzle I4 as the relief port by which the operating pressure P4 is varied, the pressure back of the nozzle Ill as varied by the operation of the baille I5 operates a relay valve generally indicated at 21. The relay valve comprises a spring-loaded bellows 21 communicating with the pressure back of the nozzle Ill and carries a baille 29 adapted to control the opening of a relief port or nozzle 30 provided in the line I2. This relief port 30 has a larger area than the nozzle I4 and so can vary the pressure in line l2 more rapidly than could the nozzle and bafe of Figure 2. A second, and larger-bore, resistance Illa is provided in the line I| a, so that the pressure in line I2 may be manipulated more conveniently by the operation of the baille 29.

With this construction the proportioning effect of the baiile and nozzle may by logical design be eliminated by making the relay valve so sensitive that for all practical purposes lt is always moving toward an open or a closed position but so fast that the resulting pulsations in the instrument are not indicated. Thus, as the valve 2l is tending to close ofi, the pressure response is felt by the baille I6 s0 quickly that before the pressure has a chance to decrease to any visible extent beyond its proper value the baille I6 causes the relay valve to throw in the reverse direction. Likewise the response of the baille Iii to the resulting pressure increase is so fast that the relay valve starts to throw in the reverse direction before any visible change in pressure above its proper value is indicated. So with this construction the pressure diierence (P1-Pa) is effectively maintained substantially constant throughout the whole range of the instrument.

The indicating bellows 2D and the measuring restriction I9 is the same as that shown in Figure 2.

Whereas the suction Icontrol valve serves to main-tain the overall sucti-on pressure approccimately constant it does not eliminate sudden changes in the suction supply pressure. In the present embodiment of the invention, however, the relay valve 21 eliminates the eliect ci such sudden changes in the suction pressure on the reading of the instrument. The relay valve accomplishes this result by increasing or decreasing the pressure P4 to compensate for decrease or increase in the suction pressure Ps1. The operation of this compensation may be traced as iollows: Assuming the pressures Pl and Pa to be balanced, if the pressure Ps1 suddenly decreases (i. e. the suction becomes greater), it will have the double eilect of trying to reduce the pressure P4 and of reducing the pressure back of the nozzle I6. But this latter reaction causes the bellows 28 of the relay valve to contract to uncover further the nozzle 3G, and hence independently to increase P4. The opposite reaction takes place if the pressure Ps1v suddenly increases.

The barometric or atmospheric pressure is brought to the instrument, as in Figure l, through a head 3 and line 2. Line 2 connects with one side 3| of a dierential pressure detecting bellows generally indicated as 32. The other bellows 33 is connected through a line 34 with the pressure P3 in the chamber IB. The baille I5 4is mounted between the movable ends of the bellows 3| and 33 and so responds to the pressure difference in the bellows. The pressure in the bellows 3| is approximately that of the true atmosandasse..

pheric pressure P1 existing at the head 3 but because of the distance in length oi duct that separates the bellows 3l from the place of measurement of the atmospheric pressure, the pressure in the bellows 3| actually lags behind the pressure P1 if the latter is changing and so the pressure in the bellows 3l will be designated as P5.

To oiset the effect of this lag a restriction 35- is provided in the line 3d between the chamber IB and the bellows 33 so that the pressure P3 always leads the pressure Pe in bellows 33 so long` the pressure P3 caused by the resistance 35 makesv the pressure P3 follow the pressure P1 instead of the pressure P5. The value of the resistance 35 is selected so that the timel constant of the resistance 35 and its'associated volume (bellows 33) effectively equals the time constant of the resistance of line 2 and its associated volume. The proper amount of resistance may be empirically obtained by connecting the atmospheric end of tube 2 and the bellows 33 through the restriction 35 to a common pressure chamber. rhe resistance 35 is then varied until, following a change in pressure in the chamber, no difference in pressure occursbetween pressures Fs and Ps.

This instrument thus is adapted to indicate accurately the changing barometric pressure. Whereas it is not shown as corrected for temperature conditions as may be desirable in some instances when used for aircraft, it does give an accurate indication oi' the rate at which the barometric pressure is changing and if the rate of change of atmospheric pressure is due to the rate of change of altitude the instrument indi- Icates the rate of change of altitude.

As shown in Figure 3, the apparatus may also be used as an improved indication of barometric pressure and so of altitude by making an ex'- rhausted or aneroid bellows 3G responsive solely to the pressure P3 in the chamber Ill. By adjusting the spring characteristic of such a bellows, the bellows may be calibrated to indicate the pressure P1 instead of the pressure P3. Using the pressure P3 to operate an altitude indicating bellows vhas the advantage that the lag in the pressure due to the restriction in the line 2l is eliminated in the pressure P3 and so this error which is usually present in altimeters is eliminatcd.

The aneroid bellows 3G may be located within the chamber IG, or, as shown in Figure 3, may be mounted in a chamber lila. connected to the chamber it by a line 3l. As shown, the bellows 36 is mounted on a suitable support 33. Through a connection 39 it operates an indicating pointer l0 cooperating with an index fil. As before, the chamber ita is provided with a transparent portion so that the pointer im and scale il may be viewed.

We have assumed above the use of suction pressure to operate the instrument, i. e., a pressure below and related to the existing atmospheric pressure. If desired, however, the instrumont muy be mutuo to operato on a positivo pressure, l. e., one above atmosphere. This would require only the reversing of the operation ofthe nozzle lll with respect to thebailieof Figure 2- to causeanincrease ofv pressure in bellows Il to uncoverfthe nozzle. No change would be required in thel structure of Figure 3 except a new adjustment of' the. nozzles I4 and 3D.

From the foregoing description it is evident that withthe-proper selection of values for the various pneumatic' capacities of the parts and the various restrictions an instrument may be built to indicate accurately the instantaneousrate of climb, or the instantaneous altitude, or both. Care must be exercised, however, to select the values above mentioned in accordance with known.

laws of pneumatica-hy operated. instruments. This may conveniently be done bysettingup the equation of the instrumente and calculating the valuesn'ec'essary tomake itoperate as above de'- scribed,` i; e., inr such amanner that it atall times functionspto maintainthepressure Pa'in thedesired relationship with respect to the'atmospheri-c pressure` whether the atmospheric lpressure has.

a rateof changeor not. Also the value ofthe measuring Aresistance I9 should be'selectedso as not to interfere with the maintenanceofrthepressure P3 but at the-same time should'be lsuiicient to provide thedesire'd pressure dii erencebetween P4 and P's` necessary for accurate: measurement or control..

The apparatus of the present invention. is particularlyf 'adaptedto control rate. of climb. (or altitude) ofzalrcraft..

Reierringto Figure 4, a novel controller embodying the .present measuring instruments for controlling the altitude or rate of climbt or. cle-.

scent of aircraft is shown; The instrument comprises the. rate; of climb` measuring apparatus diagrammatically shown in Figure 3', .a pressure responsive follow-up mechanism generally indicated at. 50, and responsive to the pressure differencev (E3-P4) a, servo-motor mechanism generally indicated at 5i adapted to -operatesuitable rate or altitude changing. means suchV asian elevater generally indicated at 52. The pressure responsive mechanism 50. comprises two sets of opposing-bellows; generally indicated,l at 53 and 5lll The opposingfb'ellows 53 comprises a-bellows 55 and' a bellows -56 respectivelysupported in a framework 57 at their far ends. The. movable adjacentv ends of the bellows react against one end of a torque lever 58. The other set of opposing bellows lill'4 comprises a bellows 59 and a bellows Silmounted in the same'mann'er that the bellows 55: and'aremounted and carrying be-A tween their adiacent ends` the `other end of the torque lever-v 58. through a line-55a with thel pressure Pr and the bellows. 5,9.Y is connected through 1in-e 59a;with the pressure P3 so that the respective pressures P4 and P3 are maintained at all times in the respectivev bellows 55 and 59.

These pressures effectively act against an adjustable spring system which ismanually adjustable to adjust the controller to maintain the desired rate of climb or descent. The spring system in the present embodiment comprises compression springs El and 6.2 respectively mounted between opposing-arms of the torque lever 58 and the opposing armsV llA and 64 of an adjustable setting; lever 65. The lever 55 is pivoted at.65a and the torque lever 58 is pivoted at T2.

With this construction the effect of the pressure P4 in-bellowsopposesthe effect of the pressure P3 in the bellows 59 and the spring system can be manually adjusted either to impart a moment to the torquelever 58l in favor of the b'ellows 55er to.v impart a torque. moment to the The'bellows 55 is connected.4

torque lever 58 in favor of the bellows 58. In other words, the bellows 55 and 58 oppose each other and the springs Bl and 52 are adjustable to change the eiect of one bellows on the other for any given pressure difference (P4-Ps).

Bellows B, opposing bellows 55, and bellows 6i), opposing bellows 59, are force balancing bellows and operate as a follow-up mechanism. Auxiliary pressure is supplied to bellows 56 and 68 in such manner as at all times to just balance the eiect of the pressures (Ps-P4) and of the spring system to maintain the torque lever 58 in a substantially neutral position. As will be described, this same auxiliary pressure is used to regulate the position of the elevator 52. l

The auxiliary pressure (Pe) supplied to the bellows 5B and the auxiliary pressure (P1) supplied to the bellows 50 is controlled by a double nozzle, single bale mechanism comprising a baiile 66 and nozzles 61 and 68. The nozzles are connected through lines 59 and 18 and resistances 89a and 18a with the suction pressure Ps. The output or back pressure of the nozzles as lmanipulated by the bafiie 65 is connected respectively through lines 1l and lla with bellows 56 and 60.

The baie S8 is loosely mounted on a shaft 12 on which the torque lever 58 is suitably mounted and is operated through oppositely disposed resilient stops 13 and 14 mounted on the hub 15 of the torque lever 58. With this construction the slightest movement of the torque lever is transmitted to the baiile 65, but if the movement is greater than that permitted by the nozzles 81 or 68 the resilient stops 13 and 14 yield to prevent straining of the parts. One of the stops 13, 1li is positively located in its normal position so that the baille 8B under normal conditions is held in a denite position with respect to the torque lever 58.

The construction of the baffles and nozzles is such as described in connection with Figures 2 and 3 and lsuch that only a slight movement of the baille is required to move it through its operating range to cause maximum pressure change back of the nozzles. It is preferably designed so that when the baffle is in neutral position equal pressures tend to build up back of the respective nozzles. The equal. pressures thus established are preferably about half-way between the minimum pressure that tends to build up back of the nozzle when covered by the baille and the maximum pres-sure that tends to build up back of the nozzle when completely uncovered by the bafile. The position relationship between the torque lever and the baille is such that the torque lever holds the baille within its operating range, as described so long as the torque lever is in its neutral position.

The baille 85, being responsive to the output pressures of the nozzles through the bellows 55 and Bi! and torque lever 58 establishes a pneumatic follow-up system by which the operating pressures Pe and P'z in the bellows 58 and 58 always balance the variable pressures P3 and P4 and the adjustable eiect of the springs 5l and 62 so that the torque lever is held stationary in its neutral position except for slight movements necessary to move the bale 65 through its small operating range. In other words, the pneumatic follow-up system constitutes a force balancing system in which the pressures Pe and Pv are maintained at whatever values are necessary to counterbalance the e'ects of the varying pressures P3 and Pi. Thus the pressures Ps with the springs 5l and reverse action takes place and P'z vary respectively and in direct proportion to the variation in the values of the pressures P4 and P3. If the rsprings 6l and 82 are so adjusted as to exert equal and opposite forces on the torque lever 58, the pressure difference between Ps and P7 equals whatever pressure difference exists between P3 and Pr and when the Aaircraft has zero rate of climb or descent, the pressure difference (P4-P3) is zero and the pressure diierence (Pe-P7) is zero. If under this condition of adjustment the aircraft acquires a rate of change such as, for example, a rate of descent then, as above described, pressure P4 becomes greater than pres-sure P3 and the pressure difference between them is proportional to the rate of descent. As the pressure diierence (P4-P3l changes from zero to its new value, the pneumatic follow-up system causes pressure Pe to increase and pressure P1 to reduce to establish a pressure difference equal to that of (P4-P3) to maintain the torque lever 58 in its neutral position. The reverse action takes place if the aircraft assumes a rate of climb.

The output pressures Ps and P1 of the two nozzles in addition to being used to establish the pneumatic feed-back system are also used to operate the dierential or servo-motor 5l. The pressure Pe back of the nozzle 51 is conducted to one side of the differential motor through a line 16 and the differential pressurev P7 back of the nozzle 88 is conducted to the other side of the differential motor through a line 11. The differentialv motor may be of any desired type and, as diagrammatically illustrated, comprises two spring-loaded bellows 18 and 19 covered respectively by covers and 8l. The bellows support a common shaft 82 connected mechanically through a yoke to operate a lever 83 which in turn is suitably mechanically connected to operate the elevator 52. With this construction,` therefore, the position of the elevators is made a function of the diierence between the output pressures Pe and P1 and in turn a function of the value of the pressure difference (Pk-P3).

When the pressure difference is zero the elevaior may be adjusted to assume aneutral position. but the servo-motor operates the elevator so that when the pressure diierence (P4- Pal becomes negative the elevators tilt in one direction from neutral an amount which is a function of the pressure difference andv when the pressure difference becomes positive the elevators tilt in the opposite direction.

Still considering the above adjustment, i; e., 82 exerting equal and opposite force on the torque lever, it is evident that if the aircraft for some reason tries to assume la rate of descent, the resulting increase of the pressure 'difference (P4-P3) causes the pressure P6 to increase and the pressure P1 to decrease causing the bellows of the differential motor to move to the right with the result that the elevator is tipped to check the tendency of the aircraft to assume a rate of descent. The if the aircraft tries to assume a rate o-f climb. The controller with this adjustment therefore tries to give the alrcraft minimum rate of climb or descent.

To adjust the controller thus described to give the aircraft a rate of descent, thefhandle 65h of the spring-loading mechanism is moved clockwise. as shown in Figure 4, to cause the spring system to put an unbalanced moment on the torque lever. This operation changes the equal or one-to-one relationship maintained by the follow-up system between the pressure difference (P4-P3) and the pressure difference (P6-P7), and thus changes the functional relationship between the pressure difference (P4-P3) and the position of the elevator.

In other words, loading the torque lever 58 unevenly to give it a moment in the clockwise direction changes the pressure difference (Ps-P7) otherwise required to balance a given pressure difference (P4-Pa) a value proportional to the unbalanced moment. The pressure difference (Pe-P7) which is thus caused to exist operates the elevator 52 to give the aircraft a rate of descent. As the aircraft assumes a rate of descent, however, the pressure difference (P4-P3) increases in proportion to the rate of descent and other conditions being equal the pressure differences (P4-P3) and (Pe-Pv), although now unequal, balance at a value which is a function of the setting of the spring system and the aircraft is given a rate of descent which is a function of the setting of the spring system. Also, other conditions being equal, as the torque lever is loaded to give it a larger moment, the rate of descent is increased and as it is loaded less unevenly the rate of descent is decreased. Likewise, as the torque lever is loaded unevenly in the reverse sense the aircraft is given a rate of rise which is a function of the spring-loading.

As described in connection with the adjustment for zero rate of climb or descent, if the controller is adjusted, for example, to give the aircraft the rate of descent and the aircraft tends to descend more rapidly than the adjustment calls for, the pressure diiference (P4-P3) increases over that which is normal for the adjustment, causing the pressure difference Pes-P1) to increase with the result that the elevator 52 is operated to check' the increased rate of descent. The reverse action takes place if the rate of descent slows down. Thus the controller tends to maintain a steady rate of descent or rise, as the case may. The controller, therefore, manipulates the elevator 52 to maintain the desired rate of rise or descent which is a function of the moment imparted to the torque arm by unequally loading the springs 6l and 62 which itself is determined [by the adjustment of the handle 65h.

In `Figure 5, the controller is shown connected up to manipulate the elevator to maintain a desired altitude. To this end, either the pressure P4 or P3 (P4 as shown) is connected to the bellows `55, but the bellows 5l? is replaced by an adjustable spring 84. The bellows 5G and 6D are provided as before and the pneumatic feed-back system is the same as in Figure 4. With this construction, when the force exerted by the pressure P4 on the torque lever 58 equals that exerted by the spring 84 the pressure difference (Pe-Pf1) is zero and the pressures Ps and P7 are equal and the elevator 52 is in its neutral position. When ne pressure P4 is steady it is proportional to the existing atmospheric `pressure and when corrected for barometric conditions is proportional to the altitude. ,Under such conditions, an aircraft on which the controller is installed would be flying at an altitude proportional to the pressure P4. If` howeverfthe aircraft starts to lose altitude, the pressure 'P4 instantly increases, as above described, and causes the pressure in bellows 56 to increase proportionally and the pressure in the bellows 6U to decrease proportionally with the result that the'elevator 5 2 is adjusted to check the descent.

The altitude at which the aircraft is thus controlled is adjustable by adjusting the compression of the spring 84 as by adjusting the threaded screw 85 supporting an adjustable support 86 of the spring 84. If, for example, the spring pressure is increased, the reaction of the pneumatic feed-back system is such that the pressure in bellows 6E! increases and the pressure in bellows 56 decreases with the result that the elevator is adjusted to cause the aircraft to descend. But as it descends, the pressure P4 increases until eventually the force exerted by P4 on the torque lever 58 balances that exerted by the spring 84 so that the controller now manipulates the elevator to maintain the aircraft at a lower altitude than that maintained by the previous adjustment.

The rate of climb or descent controller and the altitude controller thus described have the advantage of being immediately responsive to changes in altitude or to rate of change of altitude and so are adapted to manipulate the elevator or other mechanism influencing rate of climb or descent to maintain the desired condition of ilight of the aircraft. A further advantage of the controller as an altitude controller is that by making the controller responsive to the pressure P4 quantitative corrective changes in the elevator position are made not only in response to the departure of the aircraft from the desired altitude, but also in response to the rate of change of the altitude.

We claim:

l. Apparatus for measuring the rate of change of atmospheric pressure as, for example, that due to changing altitude comprising, in combination, a pressure chamber, a source of suction pressure a connection between said source and pressure chamber, valve means for controlling the flow of said suction pressure to and from said chamber to maintain the pressure therein in a predetermined relationship to said atmospheric pressure, restriction means lbetween said valve means and pressure chamber to cause .a suction pressure di'erential to exist so long as there is flow to or from said chamber, and means for measuring the suction pressure differential required to maintain said relationship.

2. Apparatus for measuring the rate of change ofatmospheric pressure as, for example, that due to changing altitude comprising, in combination, a pressure chamber, a source of suction pressure, a connection between said source and said pressure chamber, means for controlling the flow of said suction pressure to and from sai-d chamber to maintain the pressure therein in a predetermined relationship to said atmospheric pressure, a measuring restriction in said connection between said controlled ilow of suction pressure and said pressure chamber for measuring the pressure difference required to maintain said relationship, and means responsive to the pressure drop across said restriction, said means being calibrated to translate said pressure drop into rate of change of the atmospheric pressure.

3. Apparatus for measuring the rate of change of atmospheric pressure, such as, for example, that caused by changing altitude of an aircraft, comprising, in'combination, a pressure chamber, a source of suction pressure, a connection between said source and said pressure chamber, means responsive to said atmospheric pressure and to pressure in said 'pressure chamber for controlling the iiow of said suction pressure to and from said pressure chamber-to maintain the pressure therein in a predetermined relationship to said atmospheric pressure, and a metering orice in said connection between said source and said pressure chamber for establishing a pressure differential which is a function of the ow required to maintain said relationship, and means continuously responsive to the value of said pressure diierential.

-4. Apparatus for measuring the rate of change of Vbarometric pressure such as, for example, that caused by changing altitude of an aircraft, comprising, in combination, a pressure chamber, a source of auxiliary pressure, a connection between said source and said pressure chamber, control means for controlling the ilow of pressure to and from said pressure chamber to maintain the instantaneous value of the pressure in said chamber in a predetermined relationship to the instantaneous value of the barometric pressure, said control means including oppositely acting expansible members respectively connected through balanced restrictions to the pressure chamber and to a barometric pressure head, and a restriction to said flow of pressure in said connection between said source and said pressure chamber for creating a pressure dierential which is a function of the flow required to maintain said relationship whereby said differential may be utilized as a measure of the rate of change of barometric pressure, and means continuously responsive to the value of said pressure difierential.

5. In apparatus for measuring the rate of change of pressure such as that caused by the changing altitude of aircraft, in combination, a pneumatic capacity, a source of auxiliary pressure, a 'line leading from said source of auxiliary pressure to said pnetunatic capacity, control means for controlling the flow of pressure to and from said pneumatic capacity including a restriction in said line, a port to atmosphere in said line beyond said restriction, a valve for said port, mechanism for operating said valve, said mechanism being responsive to the effective pressure difference between the pressure in said pneumatic capacity and the barometric pressure whereby said valve controls the operating pressure'back of said port to maintain the pressure in said pneumatic capacity in a predetermined relationship with respect to said barometric pressure, a restriction in said line beyond said port for establishing a pressure difference between the pressure in said pneumatic capacity and the operating pressure in said line, which pressure diiierence is a function of the flow required to maintain the pressure in said pneumatic capacity and means responsive to the pressure dierence for indicating the value of the rate of change oi altitude.

'6. vIn apparatus for measuring the rate of change of altitude of aircraft by measuring the rate of change of the barometric pressure comprising, in combination, a pneumatic capacity, a source of auxiliary pneumatic pressure, a connection between said source of auxiliary pressure and said pneumatic capacity, control means for controlling the flow of pressure to and from saidv pneumatic capacity, said control means including a restriction in said connection, a port to atmosphere in said connection beyond said restriction, a valve for said port, means for operating said valve including a relatively stiff springloaded bellows responsive on one side to the pressure in said pneumatic capacity and on the other -side to the barometric pressure and adapted to operate said valve to maintain an operating pressure back of said port such as to maintain a predetermined pressure diierence between the pressure in said pneumatic capacity and said barometric pressure, a restriction in said connection beyond said port for establishing a pressure diiference between the pressure in said pneumatic capacity and the operating pressure in said connection so long as there is ow between the two pressures, and means responsive to the pressure difference for indicating the value of the rate of change of altitu-de as indicated by said pressure diierence.

7. In apparatus for measuring the rate oi change of altitude of aircraft by :measuring the rate of change of the barometric pressure comprising, in combination, a pneumatic capacity, a source oi auxiliary pneumatic pressure, a connection between said source of auxiliary pressure and said pneumatic capacity, control means for controlling the flow of pressure to and from said 'pneumatic capacity, said control means including a restriction in said connection, a port to atmosphere in said connection beyond said restriction, a valve for said port, means for operating said valve including a relatively stili spring-loaded bellows responsive on one side to the pressure in said pneumatic capacity and on the other side to the barometric pressure; a second restriction in said connection, a second and larger port to atmosphere in said connection. beyond said second restriction, avalve for said port, a spring-loaded bellows for operating sai-d valve and responsive to the pressure back of said first port as manipulated by sai-d first bellows, said second port and valve acting as a relay valve controlling the operating pressure determining the flow to and from. said pneumatic capacity whereby a predetermined pressure difference is maintained between the press re in said pneu.- matic capacity' and the barometric pressure, a restriction in said connection for establishing a pressure difference between the pressure in said pneumatic capacity and the operating pressure in said line so long as the pressure in said pneumatic capacity has a rate of change, and a spring-loaded bellows responsive to the pressure dierence for indicating the value of the rate of change of altitude as indicated bysaid pressure difference. i

8. Apparatus responsive to barometric pressure for measuring altitude of aircraft comprising, in combination, a pneumatic capacity, a source of auxiliary pressure, a connection between said source of auxiliary pressure and said pneumatic capacity, control means for controlling the flow of' pressurefto and from said pneumatic capacity including a port to atmosphere in said connection, a valve for said port, means for operating said valve including a iirst bellows connected to said pneumatic capacity, a second :bellows opposing the control action oi the rst bellows and connected to a barometric static head through an unavoidable restriction., and a restriction between sald rst bellows and said pneumatic capacity to oiset the lag caused b-y the unavoidable restriction whereby said control means maintains the instantaneous value of the pressure of said pneumatic capacity in a predetermined relationshipv with tbe instantaneous value of said barometric pressure, and means proportionally responsive to the pressure in said pneumatic capacity for indicating the altitude.

9. Apparatus responsive to barometric pressure for measuring altitude and rate of change of altitude oi aircraft comprising, in combination, a pneumatic capacity, a'source of Yauxiliary, pressure, a connection betweenisaid source of auxiliary pressure and said pneumaticrcapacity, control means for controllingithe flow of pressure to andfroni said pneumatic capacity :including 4a port to atmosphere in said oonnectioma valve for said port, means for operating said valve including a rst lbellows connected to said pneumatic capacity, a second bellows connected to a barometric pressure head through an unavoidable restriction, and a restriction between said .ilrst bellows and said pneumatic capacity to offset the lag caused .by the unavoidable restriction whereby said control means maintains the instantaneous value of the vpressureof -said pneumatic capacity in a .predetermined relationship with the instantaneous value of said barometric pressure, means proportionally responsive tothe pressure in said pneumatic capacity for indicating the altitude, and means for effectively mea-suring now to and from said pneumatic capacity and for indicating as a result of :said measurement the rate of change of altitude.

10. Apparatus utilizing changing barometric pressure for measuring rate of change of altitude of aircraft comprising, in combination, Aa pneumatic capacity, a'source of auxiliary pressure maintained at all times in a predetermined proportion with respectto the value of the barometric pressure, a connection between said source of auxiliary pressure and said pneumatic capacity, control means for controlling the ilow of pressure to and from said pneumatic capacity, said control means including a restriction in said connection, a port to'atmosphere in said connection, a valve for said port, means for operating said valve including a relatively stiff spring-loaded bellows responsive on one side to the pressure in said pneumatic capacity and on the other side to the barometric pressure: a second -restriction in said connection, a second and larger port to atmosphere in saidconnection, a valve for said port, a spring-loaded bellows for operating said valve and responsive to the `pressure back of said iirst port-as manipulated b-y said first lbellows, said `second port and valve acting as a relay valve controlling theioperating pressure determining the flow to `and from Said pneumatic capacity whereby a predetermined pressure difference is maintained `'between the pressure in said pneumatic capacity and the barometric pressure, a restriction in said connection beyond said second port for establishing a .pressure diierence between the pressure in said pneumatic capacity land the operating pressure in said line so long as said pneumatic capacity has a rate of change, and a springloaded bellows responsive to the pressure diierence for indicating the value of the rate ofchange of altitude as indicated by said pressure difference.

1l. In apparatus for controlling rate of change of altitude ci aircraft in response to barometric pressure. in combination, a pressure chamber,a source of auxiliary fluid pressure, means for controlling the flow of said auxiliary pressure to and from said pressure chamber to maintain the instantaneous value of the pressure therein at :a

fixed value with respect to the instantaneous value of the barometric pressure, means responsive to the potential of the auxiliary pressure required to maintain such relationship .for regulating the rate oi changexof altitude ofthe aircraft, said last-named means being manually adi6 iutable to set the desired rate of change of alti- 12. In apparatus for establishing a pneumatic control Vpressure for controlling aircraft yin lresponse to barometric pressure, in combination, a pressure chamber, a source of auxiliary fluid pressure, means for controlling the ow of said auxiliary pressure to and from said pressure chamber to maintain the instantaneous value 0f the pressure therein at a iixed value with respect to the instantaneous value of the :barometric pressure, means responsive to the potential of the auxiliary pressure required to maintain such relationship, valve means for controlling the supply of air to establish said pneumatic pressure, andmeans responsive to the output pressure of said valve means, and in conjunction with said responsive means and in opposite sense thereto operating said valve means to establish said pneumatic control pressure.

13. In apparatus for establishing a pneumatic control pressure for controlling aircraft in response'tobarometri-c pressure, in combinationpa pressure chamber, a source of auxiliary .uid pressure, vmeans for controlling the flow of l,said auxiliary pressure to and from said `pressure chamber to maintain `the instantaneous value of the pressure'therein at a fixed value with respect to the instantaneous value of the barometrlc pressure, means responsive to the potential of the auxiliary pressure required to maintain such relationship, valve means for controlling thezsupply of vair to establish said pneumatic control pressure, means responsive to the output pressure of saidvalve meansand in conjunction withsaid responsive means and in opposite sense 4thereto operating said vvalve means to establish said pnerunatic Vcontrol pressure, and means for adjusting the opposing relationship between said means responsive to the potential and said means responsive to the output pressure.

14. In apparatus for establishing a pneumatic control pressure controlling altitude of aircraft, in combination, a pressure chamber, a source of positive pressure, control means responsive to atmospheric pressure and to pressure in said pressure chamber for controlling the ow of said positivepressure to and from said pressure chambei to maintain the pressure therein in a predetermined relationship to said atmospheric pressure, and a restriction to'said now of positive pressure betweensaid control means and said pressure chamber, valve means for controlling the supply of pressure to establish said pneumatic control pressure, means responsive to the pressure between said control means and said restriction foroperating said valve means, and means responsive to the output pressure of said valve means and operating said valve means inopposite sense to said means responsive to the pressure between said control means and said restriction.

l5. In apparatus for establishing a pneumatic control pressure controlling altitude of aircraft, in combination, a pressure chamber, a :source of positive pressure control, means responsive to atmospheric pressure and to pressure in said pressure chamber for controlling theilow of said positive pressure 'to and from said pressure chamber to maintain the pressure therein in a predetermined .relationship to said atmospheric pressure, anda restriction to said flow of positive pressure between said' control means and said pressure chamber, `valve means for controllingithe supply of pressure to establish said pneumatic .control pressure, means responsive to the pressure between said control means and said restriction for operating said valve means, means responsive to the outlet pressure of said valve means and operating said valve means in opposite sense to said means responsive to the pressure between said control means and said restriction and means for adjusting the operating relationship between said means responsive to the pressure between said control means and said restriction, and said means responsive to the operating output presn sure of the valve means.

GEORGE A. PHILBRICK.

ALLAN R. CATHERON.

REFERENCES CITED The following references are of record in the le of this patent:

Number Certicate of Correction Potent No. 2,445,335. July 20, 1948.

GEORGE A. PHILBRICK ET A L.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 8, for bellows 27 read bellows 28; column 16, line 15, claim 12, after the word pneumatic insert control; column 17, line 4, claim 15, for outlet read output; column 18, line 15, under the references cited, for the name Qiebolz read Zz'ebolz;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent OHice.

Signed and sealed this 15th day of March, A. D. 1949.

[ Wim; w w

THOMAS F. MURPHY,

Assistant (f'ommz'ssz'oner of Patents.

Certificate of Correction Patent N 0. 2,445,335. July 20, 1948.

GEORGE A. PHILBRICK ET AL.

It is hereby certied that errors appear in the printed specification 0f the above numbered patent requiring correction as follows:

Column 6, line 8, for bellows 27 read bellows 28; column 16, line 15, claim 12, after the Word pneumatic insert control; column 17, line 4, claim 15, for outlet read output; column 18, line 15, under the references cited, for the name Qiebolz read Zebolz;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of March, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommissz'oner of Patents. 

